Post update: What is it?

The mystery object shown in my last blog post is a macro composite image of the right eye of Benjamin Franklin, as he appears on a $100 bill. The $100 bill is the largest denomination Federal Reserve note currently issued for public circulation.

Image Credit: Wikimedia Commons.

Tech Tips

2.5x magification | aperture f/4 | shutter speed 1/250 s | ISO 160

The preceding image is a focus stacked composite of 77 JPG photos taken with my Fujifilm X-T3 digital camera plus a Laowa 25mm Ultra Macro lens. The lens was set for 2.5x magnification and an aperture of f/4, the “sweet spot” for this lens.

The camera was mounted on my NiSi NM-200 manual focus rail. A safe step size of 50 microns was used in order to avoid focus banding, as determined by using Zerene Stacker DOF Calculator.

For better composition of the final composite image, I created the stack by focusing past the farthest focus point and moving the rail backward to slightly beyond the closest focus point. (Remember, the subject looks bigger at the farthest focus point than the closest. This almost certainly means it will be necessary to crop the final image if you shoot front-to-back. Going back-to-front helps to avoid this problem.)

The carriage of the focus rail traveled a total distance of 3.85 mm.

77 steps/1 x 50 microns/step = 3,850 microns

3,850 microns/1 x 1 mm/1,000 microns = 3.85 mm

77 steps is probably more than necessary but I wanted to be sure the entire image is acceptably in focus.

Helicon Focus was used to create the focus stack. The final rendering is saved as a TIF file, by default. I converted the TIF to JPG for posting in my photoblog. The final output, shown above, is unedited otherwise.

Sidebar

A micrometer (also known as a micron) equals 0.001 of a millimeter, or 1/1,000 of a millimeter. In other words, there are 1,000 micrometers in one millimeter. The symbol for micrometer is µm.

Related Resources

• Zerene Stacker DOF Calculator
• Helicon Focus – Quick Start on Mac OS, by HeliconSoft (2:20)

Copyright © 2023 Walter Sanford. All rights reserved.

Zerene Stacker DOF Calculator

The DOF Calculator featured in Zerene Stacker is by far the best tool for determining depth of field and the safe step size for focus bracketing. Rik Littlefield, creator of Zerene Stacker, recently released an online interactive version of DoF Calculator. Sincere thanks to Rik for sharing his expertise!

How to use the calculator

There are several ways to use the DOF Calculator, as shown in the following screen capture. I used two methods to calculate the “safe step size” (with 20% overlap) for focus bracketing with all of my basic macro photography rigs.

Choose Option 1 for the best quality focus stacked composite images. Set the aperture for your camera lens to its “sweet spot.”

Screen capture used with permission from Rik Littlefield.

Choose Option 4 if you are using a microscope objective for a macro lens.

As you can see in following examples, it isn’t necessary to input values for every field in the calculator.

AmScope / Reakway 4x microscope objective

Determining depth of field – safe step size for a 4x microscope objective is the simplest calculation of all my macro photography rigs. All you need to input is the “NA” (numerical aperture) that’s labeled on the side of the microscope objective. In this case, the NA equals 0.10.

Photo Credit: AliExpress / Reakway.

It’s recommended that you use a 20% overlap between steps. Input a value of 0.2 in the field for “Step overlap.”

Screen capture used with permission from Rik Littlefield.

DoF: 0.054862 mm (54.862 microns)
Step size (suggested) at 20% overlap: 0.04389 mm (43.89 microns)

Let’s apply the output from the DOF Calculator (shown above) to my relatively new NiSi Macro [manual] Focusing Rail NM-200. The larger adjustment knob is shown below. One full rotation of the knob moves the carriage one millimeter, or 1,000 micrometers (microns). The knob is marked in 100 increments, so each increment on the knob is 10 microns. Every numbered increment is 100 microns.

For my 4x microscope objective, I would turn the adjustment knob four (4) increments between shots or 40 microns (rounded down from 43.89 microns). It’s OK to use a smaller step size than the DOF Calculator recommends.

Photo Credit: B&H Photo.

Laowa 25mm Ultra Macro (at 2.5x, f/4) plus Fujifilm X-T3

The Laowa 25mm Ultra Macro lens can be set for magnifications ranging from 2.5x to 5x. The following example shows the lens set for 2.5x. Input a magnification of 2.5, and a lens F-number of 4 (an aperture of f/4 is the “sweet spot” for this lens).

Screen capture used with permission from Rik Littlefield.

DoF: 0.068854 mm (68.854 microns)
Step size (suggested) at 20% overlap: 0.055083 mm (58.038 microns)

For the Laowa 25mm Ultra Macro lens, I would turn the adjustment knob on my NiSi NM-200 five increments between shots or 50 microns (rounded down from 58.038 microns).

Fujinon 80mm macro (1x, f/8) plus Fujifilm X-T3

The Fujinon 80mm macro lens is one of the sharper lenses I own. Maximum magnification is 1:1 (life size).

Screen capture used with permission from Rik Littlefield.

DoF: 0.56306 mm (~563 microns) ← remember 1 mm = 1,000 microns
Step size (suggested) at 20% overlap: 0.45045 mm (~45 microns)

Each increment on the NiSi NM-200 manual focus rail is equal to 10 microns. For my Fujinon 80mm macro lens, I would turn the adjustment knob four numbered increments between shots — equal to a distance of 40 microns (rounded down from ~45 microns).

Canon 100mm macro (1x, f/11) plus Canon EOS 5D Mark II

The Canon 100mm macro is another one of the sharper lenses I own. Maximum magnification is 1:1 (life size).

Screen capture used with permission from Rik Littlefield.

DoF: 1.0647 mm (1064.7 microns) ← remember 1 mm = 1,000 microns
Step size (suggested) at 20% overlap: 0.85176 mm (851.76 microns)

Each numbered increment on the NiSi NM-200 manual focus rail is equal to 100 microns. For my Canon 100mm macro lens, I would turn the adjustment knob eight numbered increments between shots — equal to a distance of 800 microns (rounded down from 851.76 microns).

Canon MP-E 65mm macro lens (1-5x) plus Canon 5D Mark II

The Canon MP-E 65mm macro lens can be set for magnifications ranging from 1x to 5x. The following example shows the lens set for 3x.

Screen capture used with permission from Rik Littlefield.

DoF: 0.12251 mm (122.51 microns)
Step size (suggested) at 20% overlap: 0.098008 mm (~98 microns)

Remember, each increment on the NiSi NM-200 manual focus rail is equal to 10 microns. For my Canon MP-E 65mm macro lens set for 3x magnification, I would turn the adjustment knob nine increments between shots — equal to a distance of 90 microns (rounded down from ~98 microns).

Related Resource

What if you don’t know the magnification of the macro rig you’re using? Or maybe you add an extension tube and/or close-up filter to a 1x macro lens — how does that change the magnification of the lens?

How to measure magnification provides photo-illustrated step-by-step directions, including sample math calculations.

The Backstory

I have been working behind the scenes trying to figure out how to determine focus bracketing step size for a variety of macro photography gear that I own. I have tested many depth of field – step size calculators and all of them are fatally flawed in one or more ways except for the one in Zerene Stacker.

See How to calculate step size for a long thread of posts related to my search for the answer to what turned out to a more complex process than I imagined. Thanks to the many members of photomacrography.net, especially Rik Littlefield, who kindly and patiently answered all of my questions.

Copyright © 2023 Walter Sanford. All rights reserved.